Assessing the change of water quality and quantity in the upper basin of Thac Ba reservoir under the impacts of future land-use scenarios

Variability in land use is anticipated to affect regional hydrologic conditions and have a wide range of implications on water resources and human health across the world, particularly in developing countries like Vietnam. Land-use/land-cover change has been a significant difficulty for the social-economic development of upland areas in northern Vietnam in recent years, owing to its relationship with downstream environmental concerns such as water quantity and quality. The Geographical Information System (GIS) and SWAT model (Soil and Water Assessment Tools) were used in this study to assess the impacts of land-use change on streamflow and sediment runoff under various future development scenarios based on economic circumstances. The Thac Ba reservoir watershed was chosen for examination because it is vital for agriculture, hydropower generation, and household water supply to communities living in the watershed's proximity and downstream. It is estimated that 75-85% of the total yearly rainfall falls between May and October. When it comes to sediment runoff in the Thac Ba watershed, increasing monthly flow discharge increases mean monthly sediment runoff during the rainy season in all situations, but decreasing monthly flow discharge decreases mean monthly sediment runoff during the dry season in all scenarios. The findings demonstrated that the seasonal streamflow had been affected in a more sophisticated manner than had been observed in earlier forest conversion scenarios. Both the rainy and dry seasons saw an increase in average streamflow, which is a beneficial thing in terms of streamflow. When compared to the baseline scenario, average values in the rainy season climb by 4.72 and 8.04 percent, respectively, in scenarios 2.3 and 2.4 (extreme situations) (1.9 percent in extreme scenario). An in-depth investigation indicates that the average flow rises throughout the year, but continues to fall in November, December, and January. According to the scenarios, the most significant changes are shown in May (ranging from 2.77 percent to 15 percent) and June (ranging from 2.11 percent to 14.7 percent). Furthermore, in scenario 2.4, during dry months, the average maximum streamflow is reduced by approximately 3.5 percent in November and December, but increases in March and April.